Endocardial pacing leads may be classified in two broad categories: permanent pacing leads and temporary pacing leads. Permanent and temporary pacing leads are generally characterized in having different physical structures, materials and configurations. Structural differences between the two general types of pacing leads are driven primarily by cost considerations and the different natures of the applications for which the two types of leads are employed. Most temporary pacing leads are used for one week or less and then disposed of, while permanent pacing leads often remain implanted and functioning in patients for five years or longer.
When a permanent pacing lead is implanted in a patient, a pacemaker and an electrical connection between the pacing lead and the pacemaker are generally embedded within the body. Permanent pacing leads are commonly implanted with the aid of stylets that increase the speed and accuracy of lead electrode placement. Moreover, once the lead has been implanted and the stylet withdrawn, the remaining lead body becomes flexible and does not retain the stiffness imparted by the stylet. Thus, stylets are highly desirable and often used in permanent leads.
When implanting a permanent pacing lead, a peripheral vein such as the left or right subclavian vein is punctured by an introducer through an incised portion of the skin. A prior art “catheter” or a lead containing a stylet is inserted through the introducer. When a prior art catheter is used, the catheter's distal end is held at the apex of the right ventricle or right atrium while a temporary lead is inserted through the prior art catheter until the distal end of the lead engages and is lodged or otherwise affixed to the endocardium of the right ventricle or right atrium; the prior art catheter is then withdrawn. If a lead having a stylet is used, the distal end of the lead is guided to the apex of the right ventricle or the atrial appendage in the atrium, the lead electrode tip is affixed to the endocardium and the stylet is removed.
Temporary transvenous endocardial pacing leads are generally used prior to pacemaker implant surgery or in emergency treatment of heart arrhythmias and myocardial infarction. In temporary pacing, the distal end of a temporary pacing lead is inserted transvenously in the body using some of the techniques described above for permanent leads while the proximal end is located outside the body where electrical and mechanical connections to an external temporary pacemaker are made. The temporary pacemaker coupled to the temporary lead provides pulses of electrical energy to stimulate the endocardium through the temporary pacing lead. Typically, the temporary pacing lead is extricated from the patient when a permanent, implantable pacemaker and corresponding permanent lead are implanted, or when the need for temporary pacing no longer exists.
Epicardial pacing leads are often used in temporary pacing applications following transthoracic surgery, where the electrode is affixed to the surface of the heart. It is an advantage of endocardial leads that they typically require lower stimulation thresholds to pace the heart than those required with epicardial leads because endocardial leads provide lower stimulation thresholds over time. Temporary pacing leads should not be reused, are designed to be disposed of after a single use, and are not designed for use over prolonged periods of time.
Some ideal attributes of temporary pacing leads include: (1) small lead diameter; (2) secure placement of the tip electrode in the selected heart chamber; (3) high degree of steerability, control and torque transfer during implantation; (4) minimal damage to vein, heart valve and endocardial tissue during implantation; (5) reliable conduction of electrical impulses during use; (6) easy removal from the heart chamber with minimum tissue damage, and (7) low cost.
Secure placement of the tip electrode in the selected heart chamber is required to assure appropriate and reliable depolarization or “capture” of cardiac tissue by electrical stimuli delivered by the pacemaker or pulse generator. Known temporary transvenous leads suffer from a relatively high rate of dislodgment from sites adjacent to or on the endocardium. This is not surprising in view of the fact that no prior art temporary transvenous pacing leads utilize active fixation devices to positively secure the electrode tip to the endocardium. Instead, known temporary pacing leads rely on force provided by a bent or curved lead body as a means of pushing the distal electrode tip against endocardial tissue. If the pacing lead body or tip shifts position as a result, for example, of patient postural changes, the tip electrode may disengage or float away from the endocardium. This, in turn, may result in a loss of capture, or in a reduction of the degree of electrical coupling between the electrode and endocardium.
It is desirable that leads particularly temporary pacing leads have a high degree of steerability, control and torque transfer to permit relatively quick and accurate placement of the electrode tip at the desired site within the heart, and the initiation of temporary pacing with minimum delay and tissue trauma. Speed and accuracy of lead placement become especially important when attempting to restore a patient's heartbeat under emergency conditions. In the past, there have been a limited number of sites in the atrium and ventricle where lead placement could be effected. The accuracy of where the pacing lead is placed in the atrium or ventricle thus assumes considerable importance.
Ideally, temporary pacing leads should cause no damage to vein, heart valve and cardiac tissue during implantation. The temporary lead should have a highly flexible and soft distal tip that readily follows the direction of venous blood flow. Such directional following is often referred to as “floating” the lead or catheter through the venous system. A soft flexible distal tip on the lead or catheter may help prevent trauma to the surrounding venous and cardiac tissues as the lead is directed to the fixation site.
Temporary pacing leads should reliably conduct electrical pulses from the pacemaker even when sutures at the lead anchor suture site are drawn too tight, the lead is stressed by excessive patient movement, or when the pacemaker or attached lead is subjected to rough handling by hospital personnel. Temporary pacing leads are generally designed for a single use over a limited duration of time, and therefore are typically not constructed of materials that are as biostable, durable, strong or robust as those used in permanent pacing leads.
The technology and medicine of Implantable pacing leads, particularly temporary implantable pacing leads, are extensively discussed in U.S. Pat. No. 5,851,226 to Skubitz et al., “Temporary Transvenous Endocardial Lead” the entirety of which is incorporated by reference herein. Of particular relevance for background information regarding this invention is the disclosure of Skubitz et al. starting a column 1, line 1 through column 6 line 55, (including the Prior Art Patents listed in TABLE 1 in column 6), the disclosures of which is specifically incorporated by reference herein and is the basis for much of the discussion above.
Other disclosures incorporated by reference herein in their entireties for their background disclosures and filed as part of this application include the following:                Saulson et al., U.S. Pat. No. 4,530,368 “Temporary Bipolar Pacing Lead”;        Tarjan et al., U.S. Pat. No. 4,475,560, “Temporary Pacing Lead Assembly”;        Parsonnet, U.S. Pat. No. 4,541,440, “Bipolar Epicardial Temporary Pacing Lead”;        Barrington et al., U.S. Pat. No. 4,602,645, Atrio-Ventricular Pacing Catheter”;        Williams, U.S. Pat. No. 4,338,947, “Positive Fixation Heart Wire”        
The terms “temporary pacing lead” and “temporary lead” mean, for example, a low cost, implantable, percutaneously introduced, transvenous, endocardial lead having at least one electrode for pacing, capturing, cardioverting or defibrillating the heart at or near an endocardial site, the lead being intended for use over a relatively short and limited period of time that is usually several days in length and occasionally as long as about one month, the lead being disposed of after a single use, where the design and structure of, and materials used in, the lead correspond to the foregoing single use and low cost requirements. The terms “temporary pacing lead” and “temporary lead” include within their scopes unipolar and bipolar temporary pacing leads.
The term “active fixation” means the positive fixation of the distal end of a pacing lead, or a portion near the distal end of the pacing lead, to endocardial tissue, or through, propinquant to, or into endocardial tissue.
The term “distal” means that portion of an apparatus, or component or element of an apparatus, which is disposed in closer proximity to the end of the lead or guide catheter that is inserted first inside a patient's body during a lead implantation procedure than it is to the end of the lead or guide catheter that remains outside the patient's body during the lead implantation procedure.
The term “guide catheter” means a catheter that is designed for use in combination or in conjunction with a separate lead body, where the guide catheter forms a tubular shape and accepts the lead body inside a central lumen or tube defined by inner sidewalls, the inner sidewalls providing a bearing or load surface against which the lead body acts when one lead body end is being rotated by a physician.